1. Field
Apparatuses consistent with exemplary embodiments related to an optical system in which an illumination optical system and an imaging optical system are integrated to have a coaxial optical axis in order to obtain more precise depth information, and a three-dimensional (3D) image acquisition apparatus including the optical system.
2. Description of the Related Art
With recent advances in 3D display apparatuses and increasing demand therefor, the significance of 3D content in which depth can be perceived is becoming important. Accordingly, research into 3D image acquisition apparatuses such as 3D cameras that enable users to create 3D content on their own is increasing. 3D cameras need to have a function through which depth information along with common 2D color image information are acquired through one photographing operation.
Depth information indicating distances between the 3D camera and surfaces of an object may be acquired using stereo vision methods that use two cameras, or using triangulation methods that use structured light and a camera. However, according to these methods, the greater the camera-to-object distance, the more imprecise the obtained depth information becomes, and these methods are highly dependent on the surface states of objects. Thus, acquiring precise depth information with these methods is difficult.
To address these problems, Time-of-Flight (TOF) techniques have been introduced. TOF techniques measure a travel time of illumination light reflecting off an object after having been irradiated thereon to a light receiving unit for receiving the illumination light. TOF technology involves irradiating light having a specific wavelength (for example, near infrared rays having a wavelength of 850 nm) onto an object by using an illumination optical system that includes a light emitting diode (LED) or a laser diode (LD), receiving the light with a light receiving unit after the light is reflected off the object, and a series of process for extracting depth information, for example, by modulating the received light using a modulator with a known gain wavelength. Various TOF technologies for the series of processes are available.
In measuring distance using light reflected off an object after having been projected from an illumination optical system, the greater an amount of the reflected light that is incident on a 3D camera, the more precise obtained depth information becomes. This is because in signal processing for extracting depth information using a 3D camera, a signal-to-noise ratio is proportional to an amount of incident light, and the greater the signal-to-noise ratio, the more precise obtained depth information becomes. Therefore, an optical system needs to be designed to provide a 3D camera which receives as much incident light as possible.
A 3D camera adopting TOF technology includes, in general, an illumination optical system that emits illumination light for acquiring depth information, and an imaging optical system for acquiring an image of an object. However, since the illumination optical system and the imaging optical system are separate systems, they have optical axes that do not match. Accordingly, parallax occurs between the illumination optical system and the imaging optical system. This may cause obtained depth information about an object to be imprecise, lowering utilization efficiency of illumination light.